Risk assessment of the antibiotic amoxicillin on non-toxin-producing strains and toxin-producing strains of...

Area of Science:

• Environmental Science
• Microbiology
• Ecotoxicology

Background:

• Amoxicillin (AMX), a widely used antibiotic, contaminates aquatic ecosystems via excretion and industrial discharge.
• The ecological impact of broad-spectrum antibiotics like AMX on non-target aquatic organisms, particularly cyanobacteria, is a growing concern.
• Limited understanding exists regarding the specific risks amoxicillin poses to both toxin-producing and non-toxin-producing cyanobacteria strains.

Purpose of the Study:

• To assess the ecological risk (RQ) and physiological effects of amoxicillin on distinct strains of Microcystis.
• To compare the toxicity of AMX between non-toxin-producing (NTP) and toxin-producing (TP) cyanobacteria.
• To investigate the impact of AMX exposure on cyanobacterial growth, chlorophyll-a content, oxidative stress markers, and antioxidant enzyme activity.

Main Methods:

• Risk quotients (RQ) were calculated for amoxicillin exposure to Microcystis aeruginosa EAWAG 198 (NTP), M. aeruginosa LE3 (TP), and M. flos aquae UTEX-LB 2677 (TP).
• Physiological effects, including growth inhibition and chlorophyll-a content, were measured.
• Levels of intracellular hydrogen peroxide (H2O2), malondialdehyde (MDA), and the activity of antioxidant enzymes (glutathione-S-transferase and peroxidase) were quantified.

Main Results:

• Risk quotients indicated varying susceptibility, with Microcystis flos aquae UTEX-LB 2677 showing the highest RQ, followed by M. aeruginosa LE3, and then M. aeruginosa EAWAG 198.
• Amoxicillin exhibited higher toxicity towards toxin-producing strains compared to the non-toxin-producing strain, evidenced by lower EC50 values.
• Significant growth inhibition (p < 0.05) and reduced chlorophyll-a content were observed in exposed cultures.
• Increased intracellular H2O2 levels at 96 hours indicated significant oxidative stress (p < 0.05) induced by AMX.
• Significant variations (p < 0.05) in MDA content and antioxidant enzyme activities (GST, POD) were noted in response to AMX exposure.

Conclusions:

• Amoxicillin poses a significant risk to cyanobacteria in aquatic environments, with toxin-producing strains being more susceptible.
• AMX exposure induces oxidative stress and negatively impacts physiological parameters such as growth and chlorophyll-a content in Microcystis species.
• The study highlights the need for monitoring amoxicillin levels in aquatic ecosystems to mitigate potential ecological harm to non-target microorganisms.